Light weight medium for growing microorganisms

ABSTRACT

A light weight medium for growing microorganisms includes a mass of polymeric foam, such as a polyurethane foam, having an outer region enclosing an inner region. A plurality of fragments of an inorganic material, such as sand, are at least partially embedded in the outer region. The light weight medium may be used to support growth of microorganisms in a wide variety of biological and/or biochemical processes, or may be used without microorganisms in chemically treating wastes.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a solid carrier for supportingmicroorganism growth. More specifically, the present invention relatesto: a solid, lightweight composite polymeric medium for supportingmicroorganism growth; a solid carrier useful in catalyzing chemicalreactions and/or neutralizing acidic wastes; a solid, lightweightcomposite polymeric carrier useful in catalyzing chemical reactionsand/or neutralizing acidic wastes.

2. Description of the Related Art

Solid carriers for supporting microorganism growth, also known as growthmedia, are used in a wide variety of industries such as wastewatertreatment, production of organic compounds in bioreactors, gasseparation, biofilters, remediation of hazardous waste, water treatmentand production of fermented products. Some carriers provide an outersurface for attachment and growth of microorganisms while others allowgrowth on both the surface and on the inside of the carrier. Dependingupon the intended purpose, the microorganisms, such as bacteria, algaeand/or fungi, are used to either metabolize pollutants, synthesizespecific organic compounds from chemical reactants, or ferment sugarsinto alcohols.

In wastewater treatment, raw sewage is processed into a stream ofeffluent safe enough to discharge into a body of water. After the rawsewage is subjected to a primary treatment stage in which some of theundissolved mass is allowed to settle out, leaving “primary” waste, the“primary” is then further treated in secondary and/or tertiary treatmentstages, in which microorganisms are utilized to metabolize pollutantscontained therein, resulting in conversion of complex organic matterinto simpler organic compounds.

The treatment of the “primary” with microorganisms is often performedusing one or both of two techniques: attached growth and suspendedgrowth. In the attached growth process, microorganisms grow as a thickcoat on a porous, immobilized support media known as trickling media.The waste stream is allowed to flow over or through the support medium,which is often shaped as a bed or column, so that the microorganisms areexposed to the pollutants for metabolization. Rock media is commonlyused in such a manner.

While rock media does provide a suitable surface for the growth ofmicroorganisms, it is quite dense at around 100 lb/ft.³, and thus,relatively expensive to transport. Other less dense support media, suchas plastics, are less expensive to transport, more costly tomanufacture, and present a nonpolar surface which is not ideal as amedia for promoting population by or with a polar substance, such asmicroorganisms.

In the suspended growth process, the microorganisms move freely about asflocs in a tank in which an influent stream constantly streams in and aneffluent stream constantly flows out. In order to provide satisfactorytreatment of the waste inside the tank, it is maintained in constantturbulence. Although the flocs are relatively lightweight, duringperiods of low flow through the tank the microorganisms will tend eitherto settle out or to wash out with the flow through the tank. As aresult, the pollutants will not be metabolized into the simpler organiccompounds due to a diminished concentration of organisms.

As noted above, solid growth media are used in many other processes,such as for the production of organic compounds in a bioreactor. Incontrast to wastewater treatment, relatively pure strains of specializedmicroorganisms are employed which have the ability to synthesizespecific organic compounds. However, much as in the trickling mediaprocess for wastewater treatment, microorganisms used for organiccompound synthesis are immobilized upon a solid support in a relativelydense population. Likewise, this process also involves the same issuesregarding transportation cost versus density of the solid growth mediaand cost of manufacturing the media.

In the remediation of hazardous waste sites, specific microorganisms areused that have the ability to metabolize specific hazardous pollutantsinto simpler organic compounds. In many gas separation processes,contaminated gases are passed through a sludge containing microorganismswhich metabolize and thus remediate the pollutants. This type ofbioremediation process is disclosed, for example, in U.S. Pat. Nos.4,544,381 and 4,894,162. Similar to the suspended growth process used insecondary and tertiary wastewater treatment, low flow conditions tend tosettle out or to wash out the microorganisms.

Another common method in gas separation processes for bioremediation isto pass contaminated gases through a bed of substrates in a bioreactorwhich carries microorganisms that degrade the pollutants contained inthe gases. The prior art substrates used in this method have mainly beendecomposable organic matters, such as peat, wood chips and othercomposts. However, the use of decomposable organic matters as thesubstrates for supporting and carrying the bioremediating microorganismsmay be disadvantageous in that the substrates decompose and settle withtime. Additionally, the organic substrates are not dimensionally stableover time. Such settlement and dimensional instability change the flowpattern of the gases fed through the bioreactor, creating undesirableflow patterns, and often create channeling that directs the influentgases to bypass substantial sections of the bioreactor, diminishing theefficiency of the reactor. Moreover, the organic substrates do not haveappropriate configurations to allow the gases to pass through without asubstantial pressure drop, and the organic substrates tend to getclogged as the biomass density increases in the reactor. Therefore,bioreactors employing current organic support materials require anincreasingly high inflow pressure feeding the contaminated gases inorder to overcome pressure losses created by the microbes populating themedia.

Several solid carriers and polymeric composite products have beenproposed for a variety of reasons. For example, Japanese PatentPublication JP 6-190385 discloses a bacterial carrier made by foaming aninorganically filled polyethylene or polypropylene. U.S. Pat. No.5,503,738 discloses a macroporous substances coated with an adsorbent.U.S. Pat. No. 5,590,499 discloses an insulating wall element, wherein amixture of sand and polyurethane fills in between regularly spaced brickfillets. Japanese Patent Publication Nos. JP 55-44866 and JP 6-296500,as well as German Patent Publication No. DE 37 04 802 A1, disclose othercarriers and/or polymeric composite products. United States PublishedPatent Application Nos. US 2001/0002313 A1 (bioreactor media pellets)and US 2002/0015986 A1 (method for reducing the bioavailability of lead)disclose still other carriers and/or polymeric composite products. U.S.Pat. Nos. 3,232,865 (method for purifying wastewater), 3,646,715(prefabricated building panel), 4,005,035 (high density rigidpolyurethane foam products), 4,236,569 (foundry mold), 4,781,781 (solidpolymeric material), 4,983,299 (removal of phenols from wastewater by afixed bed reactor), 5,000,853 (biological treatment of sewage),5,217,616 (removal of organic pollutants from water), 5,503,738(biological remediation of vaporous pollutants), 5,863,789(microorganism carrier for soil remediation), 5,962,309 (microorganismcarrier for a fluidized bed) and U.S. Pat. No. 6,293,045 B1(biodegradable mulch mat) disclose still other carriers and/or polymericcomposite products.

None of the above inventions and patents, taken either singularly or incombination, is seen to describe the instant invention as claimed. Thusa light weight medium for growing microorganisms solving theaforementioned problems is desired.

SUMMARY OF THE INVENTION

The invention is a light weight medium for growing microorganisms. Themedium includes a mass of polymeric foam, such as a polyurethane foam,having an outer region enclosing a core. The medium further includes aplurality of fragments, such as sand, of a treating material directlyadhered to the polymeric foam on an outer surface of the outer region. Afirst portion of the fragments are adhered to the outer region, while asecond portion of the fragments are at least partially embedded in theouter region and a third portion of the fragments are wholly embedded inthe outer region. While the medium is particularly useful in supportingthe growth of microorganisms, it may also be used in the absence ofmicroorganisms, such as in the chemical treatment of wastes. The mediummay be made by providing a plurality of fragments of a treatingmaterial, a not fully cured mass of polymeric foam, and applying thefragments to an outer region of the mass of foam.

Accordingly, it is a principal object of the invention to provide amicroorganism growth medium that is lightweight.

It is another object of the invention to provide a microorganism growthmedium that does not require an increasingly higher inflow pressure toovercome pressure losses created by the microbes populating the media.

It is a further object of the invention to provide a microorganismgrowth medium that will not settle out of a suspended growth processduring periods of low flow, and retrofits the suspended growth processwith a growth medium that supports an attached growth process.

Still another object of the invention is to provide a microorganismgrowth medium that is stable over time and will not decompose, rot orsubstantially change dimensions.

It is an object of the invention to provide improved elements andarrangements thereof for the purposes described which is inexpensive,dependable and fully effective in accomplishing its intended purposes.

These and other objects of the present invention will become readilyapparent upon further review of the following specification anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The single drawing FIGURE is cross-sectional view of a mass of polymericfoam with granular material embedded in an outer region thereof,according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a light weight medium for growth ofmicroorganisms. While the medium, or carrier, is particularly suitablefor supporting the growth of microorganisms, the medium, or carrier, mayalso be used without microorganisms. For example, the medium may used toprovide a substrate having catalytic sites, and/or to provide asubstrate having substances for neutralization of acids.

The medium offers many advantages over prior art microorganism supportmedium and prior art polymeric composite products. It is relativelylightweight, resulting in relatively low transportation costs as well aseasy handling properties. The density of the medium may be varied inorder to suit the desired function. For example, it may be made lightenough to float in an aqueous environment or heavy enough to sink.Materials used for components of the medium may also be varied to suitthe intended function. The medium's properties may be widely varied.Physical, electrical and chemical properties, such as surface area,chemical reactivity, conductivity, chargeability, etc. may be optimizedby selecting the appropriate material. Again, depending upon the desiredfunction, the medium may be rendered relatively chemically inert andstable over time. Finally, the medium is relatively inexpensive tomanufacture.

As best shown in the FIGURE, the medium 1 includes a core of polymericfoam 3 and an outer region of a combination of a plurality of fragmentsof a treating material 2 and more polymeric foam 3. The treatingmaterial 2 includes fragments whose outer surface adheres to an outersurface of the polymeric foam 3 in the outer region, fragments oftreating material 2 that are partially embedded in the foam 3 of theouter region, and fragments of treating material 2 wholly embedded inthe foam 3 of the outer region. Preferably, no fragments are containedwithin the core, i.e., the core contains only foam and other suitableadditives.

The polymeric foam 3 may be any foamable or foam-forming syntheticresin, including but not limited to: a polyurethane, a polystyrene, apolyolefin, copolymers thereof, and mixtures thereof. If a polyolefin isselected, a polyethylene, a polypropylene, their copolymers, or amixture thereof is preferred. Preferably, the synthetic resin is apolyurethane or a polystyrene. More preferably, the polymeric foam 3 ispolyurethane. Most preferably, the polymeric foam 3 is a polyurethanethat is the reaction product of an organic isocyanate and any one of awide variety of hydroxyl terminated polyols in the presence of asuitable blowing agent. In most cases, one should select a polymericfoam 3 able to withstand a temperature of up to 500° F. Otherwise, ifthe foam is to be used in an environment having a higher temperature, ahigh temperature foam may be substituted. When a polyurethane foam isselected as the polymeric foam 3, the medium 1 offers the advantages oflow chemical reactivity, low density, low compressibility, stabilityover time, and resistance to rotting, decomposition and changes inphysical dimensions.

Preferably the treating material 2 is an inorganic material. Manyinorganic materials may be utilized, including any insoluble, or slowlysoluble, hard material of small size. Such materials include, but arenot limited to: sand, rock chips, limestone, CaCO₃, aluminum oxides,clay, textile fibers, activated carbon, pure elements (iron, aluminum,magnesium, etc.), and the like. Those skilled in the art will note thatthese materials are suitable for allowing localized electric charges ontheir surfaces, similar to surface characteristics of rock media,thereby attracting polar substances. They will also recognize that thesematerials have absorption and adsorption characteristics beneficial forsupporting growth of microorganism. They will further recognize that thechargeable, adsorptive and/or absorptive characteristics of thesematerials result in an excellent source of sites for catalysis ofchemical reactions.

When the medium 1 is used to treat wastes containing an undesirablelevel of phosphates, the treating material 2 preferably includes amaterial that reacts with the phosphates to produce a product that ismore easily treated. For example, CaCO₃ will react with phosphates toproduce calcium phosphates, while reaction with aluminum oxides willproduce metal phosphates, or aluminum phosphates.

The size of the fragments of treating material 2 may be varied in orderto suit the particular function of the medium 1 that is desired. Forexample, if a medium with a relatively low density is desired, theparticle size of the treating material 2 is relatively small.Conversely, if a greater density is desired, the particle size of thegranular material is increased. Also, if a larger total surface area ofgranular material is desired, the particle size of is increased. If agranular material of relatively large particle size is selected, betterresults for the medium are achieved if a foam of relatively greaterdensity is employed. Otherwise, the higher weight of the granularmaterial may tend to reduce adhesion between the polymeric foam andgranular material, as well as overall strength and rigidity of themedium.

The particle size of the fragments of treating material is preferably inthe range of from about 0.05 mm to about 15 mm. More preferably, theparticle size is either from about 0.2 mm to about 2 mm. Anotherpreferred particle size is from about 5.0 mm to about 14 mm. Aparticularly preferred treating material is sand having a particle sizeof from about 0.2 mm to about 2 mm. Another particularly preferredtreating material is rock chip having a particle size of about ⅜″ orless than ⅜″.

The density of the medium 1 may be varied in order to suit the desiredfunction. For example, if the medium 1 is used as a substitute for rockmedia, as described above, the density of the medium is from about 2lb./ft³ to about 6 lb./ft³ Preferably, the density is from about 3lb./ft³ to about 5 lb./ft³ Most preferably, the density is about 4lb./ft³. Because of the much lower density, a tremendous difference inshipping costs may be realized. For example, conventional rock media canhave a density of around 100 lb./ft³, while the particularly preferreddensity of the medium 1 is only 2% that of rock media. Additionally, thelighter medium 1 is much easier to handle and arrange. When the medium 1is substituted for rock media, the relatively low density of the medium1 allows a container housing it to be made from a wide variety ofmaterials. In contrast, the relatively high density of rock media oftenrequires that rock media be contained in a concrete or steel tank.

When the medium 1 is used to support growth of microorganisms duringwastewater treatment, the microorganism selected depends upon theparticular stage of treatment. In secondary treatment, microorganismssuch as zoogloea ramigera, other heterotrophic bacteria, protozoa,rotifers, nitrosomonas and nitrobacter are used to reduce complexorganic material in the waste stream into more easily treatable chemicalcompounds, such as water, carbon dioxide, nitrates and phosphates. Intertiary treatment, microorganisms such as pseudomonas, micrococcus,achromobacter, bacillus, lactobacillus, spirillum, hyphomicroblum,agrobacterium, acinetobacter, propionibacterium, rhizobium,corynebacterium, cytophagy, thiobacillus, and alcaligenes further reducenitrates, nitrites and phosphorus into nitrogen, carbon dioxide andwater.

When the medium 1 is used for supporting growth of microorganisms foruses other than wastewater treatment, such as in water treatment,bioremediation, production of organic compounds and fermentation, any ofa wide variety of microorganisms may be used. Suitable microorganismsinclude but not limited to bacteria, algae, fungi and protozoa.

The medium 1 is also useful in processes not involving the growth ofmicroorganisms, such as in mine drainage treatment and catalysis ofchemical reactions. Watery mine wastes often include metals and saltsthat lower the pH to a level requiring it to be treated or neutralizedbefore discharging it into a body of water in compliance with state andfederal laws and regulations. For such wastes, the medium 1 preferablyutilizes a caustic treating material 2 such as limestone which is usefulin neutralization of the acidic waste.

The medium 1 may be made according to the following method. A depressionis made in a bed of treating material 2, such as sand. The foamreactants, such as an isocyanate and an hydroxyl terminated polyol inthe presence of a suitable blowing agent, are then allowed to foam inthe depression. Treating material 2 is then applied to the less thanfully cured foam. Application of the treating material 2 to the foam 3is performed in such a manner so that none of the treating material 2 isintroduced into the innermost portion of the foam 3. As illustrated inFIG. 1, the fragments of treating material 2 are randomly/irregularlydistributed in the outer region of foam 3 in the finished product. Themedium 1 thus formed is then allowed to fully cure. Finally, excesstreating material 2 is removed from the medium 1. The shape of themedium 1 may be widely varied, such as a sphere, a cylinder, ovoid, apancake, or combinations of the above. The inventors have found that theshape of the medium may be varied by controlling the shape of thedepression by adjusting the humidity level in the environmentsurrounding the bed of treating material 2. The shape of the media 1 ofthe present invention increases water holding capacity when compared toconventional manufactured growth media. Channeling and flow throughdiscrete paths is dramatically reduced in the growth medium 1 of thepresent invention. Surprisingly, it has also been found that no adhesiveis necessary to adhere the treating material 2 to the polymeric foam 3,so additional steps of mixing in an adhesive found in some prior artproducts are not needed.

The medium 1 is not limited to the uses described above. For example, itmay be used in distillation, air-scrubbing towers, flue gas scrubbers,animal waste treatment, aquarium treatment systems, pharmaceuticalmanufacturing, odor control at wastewater treatment plants (such as in abiofilter at the headworks of the plant) or manufacturing plants,biofilters, fluidized beds, catalytic beds and storm water treatment.

It is to be understood that the present invention is not limited to theembodiments described above, but encompasses any and all embodimentswithin the scope of the following claims.

1. A method for producing a carrier for supporting microorganism growth, comprising the steps of: providing a plurality of fragments of an inorganic material; providing a mass of a less than fully cured polymeric foam; and applying the plurality of fragments to an outer region of the mass of polymeric foam, wherein: a core enclosed by the outer region contains none of the fragments; and said applying step is performed such that the fragments are irregularly distributed in and on the outer region.
 2. The method of claim 1, further comprising the steps of: selecting a polyurethane foam as the polymeric foam; and selecting sand having a particle size of from about 0.2 mm to about 2 mm as the fragments of inorganic material. 